Most conventional high speed cable uses an internet paddle card (also referred to as interposer) to make a transition from cable to connector. The paddle card is commonly a PCB substrate that has pads on one end to accommodate cable soldering. The other end of the paddle card has electrical terminals, such as gold-finger or contacts, for mating with another connector (e.g., a QFSP connector, SAS connector, CFP connector).
Most conventional cable connectors are satisfactory for data rates less than 15 Gbps, but are unsuitable for use to transmit data at anything greater than 15 Gbps. FIG. 1 shows a perspective view of a prior art cable connector 1 and FIG. 2 is a side view of the cable connector 1 shown in FIG. 1. FIG. 3 is section view of the cable connector shown FIG. 1 taken along line 3-3.
The prior art cable connector 1 includes cables 2A, 2B, 2C that are soldered onto a paddle card 3, which could be either PCB or FCB substrate. The ends 4A, 4B, 4C of the cables 2A, 2B, 2C are stripped-off to expose the conductors 5A, 5B, 5C, insulators 6A, 6B, 6C, and ground shields 7A, 7B, 7C. The conductors 5A, 5B, 5C are soldered onto the signal pads 8A, 8B, 8C, and the ground shields 7A, 7B, 7C are soldered onto a ground pad 9.
It should be noted that although only three cables 2A, 2B, 2C are shown in FIGS. 1-3, any number and type of cables are typically included in a prior art cable connector 1. As an example, the total number of cables may be an even number of cables such that one half of the cables are transmitting cables and the other half of the cables is receiving cables.
One of the drawbacks with the prior art cable connector 1 is that there are sections S between the ground shields 7A, 7B, 7C and the conductors 5A, 5B, 5C that are unshielded. The impedance of the unshielded sections S (see FIG. 2) is not well-controlled which may result in an unwanted increase in impedance.
This impedance discontinuity may significantly increase return loss and insertion loss. Return loss should be minimized through impedance matching to prevent signal reflections, and insertion loss should also be minimized to ensure proper signal transmission through the cable-to-board interface. Ideally, this interface should appear electrically transparent and permit signals to pass through unaltered. A properly designed ground structure may provide the necessary impedance tuning to lower return and insertion loss.
Another drawback with the prior art cable connector 1 is the lack of shielding between adjacent cables 2A, 2B, 2C. Without proper ground shielding, signaling from one differential pair may couple into an adjacent pair in the form of crosstalk, which can be very detrimental to signal integrity. Ideally, signaling from each differential pair should be completely isolated from its neighboring pair. The aforementioned ground structure design proposal can serve a second purpose in minimizing crosstalk as well.